JP7493922B2 - Oscillators, imaging devices - Google Patents

Description

The present invention relates to an oscillator and an imaging device.

As a small oscillator that generates terahertz waves, which are electromagnetic waves (radio waves) in any frequency band between 30 GHz and 30 THz, there is an oscillation circuit having a configuration including a negative resistance element such as a resonant tunneling diode (RTD), as described in Patent Document 1. In this configuration, as shown in FIG. 14(A), the oscillation circuit 100 has a negative resistance element 101, a capacitor 102, and an inductor 103. Here, a voltage bias circuit 200 is connected to the oscillation circuit 100 so that the negative resistance element 101 applies a voltage value having negative resistance characteristics.

JP 2011-61276 A

When the oscillator is used as lighting for a terahertz camera, multiple oscillation circuits (resonators) are arranged in an array in order to uniformly irradiate a wide area with terahertz waves. For this reason, multiple oscillation circuits are configured to be driven by the same voltage bias circuit. However, when a voltage is applied to multiple oscillation circuits by one voltage bias circuit using the technology described in Patent Document 1, electromagnetic waves that are not of the desired frequency may be generated due to inappropriate oscillation between the oscillation circuits (resonators).

The present invention aims to enable proper oscillation in an oscillator that applies voltage to multiple resonators using a voltage bias circuit.

One aspect of the present invention is a method for producing a composition comprising the steps of:
A plurality of resonators each having a negative resistance element;
a voltage bias circuit that applies a voltage to the plurality of resonators;
a shunt element disposed in parallel with any one of the plurality of resonators with respect to the voltage bias circuit;
having
the plurality of resonators are connected in parallel to the voltage bias circuit via separate inductors,
At a predetermined frequency or higher, the impedance of the inductor is greater than an absolute value of the impedance of a resonator among the plurality of resonators that corresponds to the inductor;
In the shunt element, a resistive element and a capacitive element are connected in series.
The oscillator is characterized by the above.
One aspect of the present invention is a method for producing a composition comprising the steps of:
A plurality of resonators each having a negative resistance element;
a voltage bias circuit that applies a voltage to the plurality of resonators;
having
the plurality of resonators are connected in parallel to the voltage bias circuit via separate inductors,
At a predetermined frequency or higher, the impedance of the inductor is greater than an absolute value of the impedance of a resonator among the plurality of resonators that corresponds to the inductor;
A plurality of shunt elements are connected in parallel to each of the plurality of resonators,
The plurality of shunt elements are connected to each other via the inductor.
The oscillator is characterized by the above.

According to the present invention, an oscillator that applies voltage to multiple resonators using a voltage bias circuit can achieve proper oscillation.

FIG. 1 is a circuit diagram of an oscillator according to a first embodiment. 4 is a graph showing the voltage-current characteristics of the negative resistance element according to the first embodiment. 4 is a circuit diagram illustrating an oscillator according to a comparative example and embodiment 1. FIG. FIG. 11 is a diagram illustrating an oscillator according to a second embodiment. FIG. 11 is a diagram illustrating an oscillator according to a second embodiment. FIG. 11 is a diagram illustrating an oscillator according to a third embodiment. 13A to 13C are diagrams illustrating an inductor according to a third embodiment. FIG. 11 is a circuit diagram of an oscillator according to a fourth embodiment. FIG. 13 is a circuit diagram of an oscillator according to a fifth embodiment. FIG. 13 is a diagram illustrating an oscillator according to a sixth embodiment. 13A and 13B are diagrams illustrating an oscillator according to a sixth embodiment. 13A and 13B are diagrams illustrating an oscillator according to a seventh embodiment. 13 is a diagram illustrating an imaging device according to an eighth embodiment. FIG. FIG. 1 illustrates a conventional oscillator.

The following describes embodiments of the present invention with reference to the drawings. However, the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the gist of the present invention.

<Embodiment 1>
First, an oscillator 1 according to the first embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram (circuit diagram) for explaining the oscillator 1. The oscillator 1 includes three oscillation circuits 100, three inductors 120, a voltage bias circuit 200, a wiring 210, wirings 211 to 213, and a common wiring 220. The three oscillation circuits 100 have the same configuration and are the oscillation circuit 111, the oscillation circuit 112, and the oscillation circuit 113, respectively. In addition, each of the oscillation circuits 111 to 113 is connected to the inductor 120. The inductors 120 connected to the oscillation circuits 111 to 113 are the inductors 121 to 123, respectively. The wiring 210 and the common wiring 220 are connected to the voltage bias circuit 200. The oscillation circuits 111 to 113 are connected to the wiring 210 by the wirings 211 to 213, respectively.

In this embodiment, multiple oscillation circuits 100 are connected to one voltage bias circuit 200. Specifically, three oscillation circuits 100, 111, 112, and 113, are connected in parallel to the voltage bias circuit 200. However, the number of oscillation circuits is not limited to three, and may be any number as long as the voltage bias circuit 200 can drive the number of oscillation circuits. In addition, although the oscillator 1 is described as being configured by a pair of the voltage bias circuit 200 and multiple oscillation circuits 111 to 113, this embodiment is not limited to this. This embodiment can also be applied to an oscillator having multiple such pairs, with the voltage bias circuit 200 and multiple oscillation circuits as one pair.

[About the oscillator circuit]
The oscillator circuit 100 will be described below. As described above, the oscillator circuits 111, 112, and 113 are each the oscillator circuit 100 and have the same configuration. The oscillator circuit 100 is a resonator (terahertz oscillator circuit) composed of a negative resistance element 101, a capacitance 102, and an inductor 103. When an operation voltage Vop is applied by a voltage bias circuit 200, the oscillator circuit 100 oscillates between 30 GHz and 30 THz to generate a terahertz wave. In the following, oscillation at a desired frequency ft determined mainly by the design parameters of the oscillator circuit is referred to as "terahertz oscillation".

A voltage-controlled negative resistance can be used for the negative resistance element 101. Specifically, by using a current-injection type resonant tunneling diode (RTD) as the negative resistance element 101, an oscillation circuit 100 capable of oscillating at terahertz frequencies can be configured. This resonant tunneling diode (hereinafter, RTD) is configured with a quantum well made of GaAs, InGaAs/InAlAs.

2A is a schematic diagram illustrating the current-voltage characteristic of the negative resistance element 101. The horizontal axis shows the voltage Vr applied to the negative resistance element 101, and the vertical axis shows the current Ir flowing through the negative resistance element 101. In the voltage-current characteristic of the voltage applied between both terminals (anode, cathode) of the negative resistance element 101 and the current flowing through it, the negative resistance element 101 can be divided into a region PR where the current value increases with increasing voltage and a region NR where the current value decreases with increasing voltage. This region NR where the current value decreases with increasing voltage is the region that has the characteristics of negative resistance. Hereinafter, the region NR will be called the "negative resistance region" and the region PR will be called the "resistance region". It is designed so that the voltage value (operation voltage Vop) in the negative resistance region NR is applied between both terminals of the negative resistance element 101 to oscillate at the desired terahertz frequency ft between the negative resistance element 101 and the capacitor 102 and inductor 103. When the operation voltage Vop changes, the oscillation conditions (frequency, output magnitude, etc.) change, so it is necessary to apply a constant voltage value to the negative resistance element 101. Note that, in order to increase the stability of the oscillation, it is desirable for the applied voltage value to be a value near the center of the voltage range of the negative resistance region NR. However, this is not limited to this, and terahertz oscillation is possible even if any other voltage is applied to the negative resistance element 101 as long as it is within the negative resistance region NR.

The current value flowing through the negative resistance element 101 when the operation voltage Vop is applied is Iop. The specific value of the operation voltage Vop varies depending on the parameters of the negative resistance element 101, but is often in the range of approximately 0.5 to 1.5 volts (V). On the other hand, the specific value of the current value Iop also varies depending on the parameters of the negative resistance element, but is often in the range of approximately 20 to 150 milliamperes (mA). However, this embodiment is not limited to the voltage value range of the operation voltage Vop and the current value range of the current value Iop described above, and can be used outside the above ranges as well.

The negative resistance value Rnr of the negative resistance element 101 will be explained using FIG. 2(B), which shows the same voltage-current characteristic as FIG. 2(A). The slope value (Va/Ia) in the voltage-current characteristic when the operation voltage Vop is applied can be set as the negative resistance value Rnr of the negative resistance element 101. The negative resistance value Rnr varies depending on the parameters of the negative resistance element 101, but is generally between 1 Ω and several tens of Ω.

As described above, in order to apply the operation voltage Vop to the negative resistance element 101, the oscillation circuit 100 is connected to the voltage bias circuit 200. Specifically, the voltage bias circuit 200 outputs a voltage Vb and applies the operation voltage Vop to the oscillation circuit 100 via wiring. Therefore, taking into account the voltage drop VΔ that occurs in the wiring between the voltage bias circuit 200 and the oscillation circuit 100, the voltage Vb is set so that the operation voltage Vop is applied to the oscillation circuit 100 (Vb = Vop + VΔ).

As shown in FIG. 1, each of the oscillator circuits 111, 112, and 113 is connected to the voltage bias circuit 200 via one of the inductors 121, 122, and 123. Here, in the oscillator circuit 111, one terminal A is connected to the voltage bias circuit 200 via the wiring 211, the inductor 121, and the wiring 210. Meanwhile, the other terminal B of the oscillator circuit 111, which is different from the terminal A, is connected to the voltage bias circuit 200 via the common wiring 220. Similarly, the terminals A and B of the oscillator circuits 112 and 113 are connected to the voltage bias circuit 200.

[Comparative Example to the Present Embodiment]
In the following, an oscillator that is a comparative example of the oscillator 1 according to the present embodiment will be described, and problems that arise in the oscillator of the comparative example will be described. In the following, the impedances of the oscillation circuits 111, 112, and 113 are Zr1, Zr2, and Zr3, respectively.
The impedances of inductors 121, 122, and 123 corresponding to oscillator circuits 111, 112, and 113 are respectively designated as Zl1, Zl2, and Zl3.

First, as a comparative example, the oscillation of the oscillator circuit 111 in a configuration that does not include the inductor 120 (121) will be described using FIG. 3(A). In the comparative example, it appears that a circuit 301 in which the oscillator circuits 112, 113, and the voltage bias circuit 200 are arranged in parallel is connected to the oscillator circuit 111. If the value of the composite impedance Z301 of the circuit 301 is sufficiently high with respect to the impedance Zr1, the oscillator circuit 111 is not affected by the circuit 301. Therefore, the oscillation frequency ft is determined only by the elements of the oscillator circuit 111 (negative resistance element 101, capacitance 102, inductor 103). However, if the value of the composite impedance Z301 is close to Zr1 or lower than Zr1, the oscillator circuit 111 is coupled to the circuit 301.

Here, although the oscillator circuits 111, 112, and 113 have the same design parameters, their actual characteristics are slightly different in a strict sense. For example, the oscillation frequency and phase of each oscillator circuit 100 are slightly different in a strict sense. Therefore, if the oscillator circuits 100 are coupled to each other, they will not be able to oscillate at the desired terahertz frequency ft due to the difference in frequency and phase. On the contrary, there is a high possibility that oscillation will occur at a frequency other than the desired terahertz frequency ft due to coupling. This oscillation at a frequency other than the desired terahertz frequency ft is called "parasitic oscillation." If such parasitic oscillation occurs, it will be even more difficult to obtain oscillation at the desired terahertz frequency ft.

In the comparative example, when multiple oscillator circuits 100 are connected to one voltage bias circuit 200, coupling between the multiple oscillator circuits 100 is very likely to occur. In addition, the oscillator circuits 112 and 113 themselves have almost the same impedance as the oscillator circuit 111 (Zr1 = Zr2 = Zr3). Therefore, the combined impedance of the parallel circuit of the oscillator circuits 112 and 113 is about half the impedance Zr1 of the oscillator circuit 111 (Zr1/2). Even if the voltage bias circuit 200 exists in parallel with other elements in the circuit 301, it does not increase the impedance Z301 of the circuit 301, so the impedance Z301 does not take a value higher than Zr1/2. Therefore, in the comparative example, Zr1>Z301 is established, so parasitic oscillation due to coupling between the oscillator circuit 111 and the circuit 301 is very likely to occur.

On the other hand, FIG. 3(B) shows a configuration in which a single oscillator circuit 111 is connected to one voltage bias circuit 200. In FIG. 3(B), it appears that a circuit 300 in which only the voltage bias circuit 200 is arranged is connected to the oscillator circuit 111. Since the composite impedance Z300 of the circuit 300 is determined by the impedance of the voltage bias circuit 200, if the impedance of the voltage bias circuit 200 is selected to an optimal value, coupling can be prevented, thereby reducing the possibility of parasitic oscillation.

As described above, in a configuration in which multiple oscillator circuits 111, 112, and 113 are connected to the same voltage bias circuit 200, there is a problem that the possibility of parasitic oscillation is higher than in a configuration in which the oscillator circuit 100 and the voltage bias circuit 200 are used one-to-one.

[Regarding the oscillator of this embodiment]
Next, an oscillator 1 according to this embodiment, which solves the problems in the comparative example, will be described with reference to Fig. 3C. In the oscillator 1, the oscillation circuits 111, 112, and 113 are connected to the same voltage bias circuit 200 via different inductors 120 (121, 122, and 123).
In the circuit 311, a set of an oscillator circuit 112 and an inductor 122 connected in series, a set of an oscillator circuit 113 and an inductor 123 connected in series, and a voltage bias circuit 200 are arranged in parallel.

In this embodiment, the impedances Zl1, Zl2, and Zl3 of the inductors 121, 122, and 123 are larger than the impedances Zr1, Zr2, and Zr3 of the oscillator circuits 111, 112, and 113 (Zl1 = Zl2 = Zl3 > Zr1 = Zr2 = Zr3). Here, the composite impedance of the circuit 310 is Z310, and the composite impedance of the circuit 311 is Z311. Since the circuit 310 is configured by arranging the inductor 121 and the circuit 311 in series, Z310 is the sum of Zl1 and Z310. In this embodiment, since Zl1 of the inductor 121 is larger than Zr1 of the oscillator circuit 111, coupling between the oscillator circuit 111 and the inductor 121 can be prevented, and the probability of parasitic oscillation occurring can be reduced. Furthermore, since inductors 122 and 123 are arranged in parallel in circuit 311, if the impedance of voltage bias circuit 200 is set to an optimal value (sufficiently high value), Z311 can obtain a value equal to or greater than half the sum of Zr1 and Zl1. In other words, Z311 can have a value larger than Zr1, so coupling between oscillator circuit 111 and circuit 311 can also be prevented. Therefore, Z310 can have a value sufficiently larger than Zr1 (a value larger than Zr1 x 2), so even in a configuration in which multiple oscillator circuits are connected, parasitic oscillation due to coupling can be sufficiently suppressed.

In addition, in this embodiment, inductors 121, 122, and 123 are arranged between the oscillation circuits 111, 112, and 113 and the voltage bias circuit 200. Since the inductor 120 has a low impedance at low frequencies, the output voltage Vb from the voltage bias circuit 200 does not drop significantly due to the inductor 120 from DC to low frequencies. Here, since the impedance Zr1 of the oscillation circuit 111 is generally about 1 Ω to 10 Ω, it is desirable that Zl1 be in the range of several tens of milliΩ to several hundreds of milliΩ near DC in order to make the bias voltage Vb and the operation voltage Vop almost equal. Note that this embodiment is not limited to this range, and any value can be used as long as it is within a range that does not cause problems in use. The bias voltage Vb may be set taking into account the voltage drop at the inductor 120.

On the other hand, the inductor 120 has a large impedance value at high frequencies. Specifically, the impedance of the inductor 120 increases in proportion to the frequency. Therefore, the impedance of the inductor 120 is sufficiently large from the lower limit frequency fs at which parasitic oscillation is possible to the terahertz frequency region, so that it is possible to prevent coupling between the oscillation circuits 100. Note that the impedance relationship (Zl1 = Zl2 = Zl3 > Zr1 = Zr2 = Zr3) described using FIG. 3(C) only needs to be satisfied in the region above the lower limit frequency fs (above a specified frequency), and does not need to be satisfied at direct current or low frequencies in the vicinity thereof. Here, the lower limit frequency fs at which parasitic oscillation occurs varies depending on the parameters of the oscillation circuit 100, but is typically between several tens of KHz and several tens of MHz. Therefore, if the frequency fs is set to 10 KHz (if Zl1 = Zl2 = Zl3 > Zr1 = Zr2 = Zr3 is satisfied at frequencies above 10 KHz), it is possible to sufficiently suppress parasitic oscillation. In addition, this frequency fs is affected not only by the oscillator circuit 100, but also by parasitic elements of the wiring and voltage bias circuit 200, so the value (inductance) of the inductor 120 can be set by calculating the frequency fs based on the parameters for actual use.

In this way, by using the inductor 120 between the oscillator circuit 100 and the voltage bias circuit 200, it is possible to easily apply voltage at frequencies below fs while simultaneously preventing parasitic oscillation at frequencies above fs.

In addition, the value of the inductor 120 (121, 122, 123) in this embodiment varies depending on the parameters of the oscillator circuit 100 used, the oscillation frequency of the terahertz wave, the wiring form, the configuration of the voltage bias circuit, etc., so it is possible to respond by selecting the optimal value at each time. As a typical example, the value (inductance) of the inductor used can be in the range from several hundred nanohenries to several microhenries. The inductor value is not limited to this, and other values can be used in the same way as long as they satisfy the conditions described in this specification.

In addition, in this embodiment, in order to separate the oscillation circuits 111, 112, and 113, the inductors 121, 122, and 123 are arranged only on the terminal A side. On the other hand, the inductor 120 is not arranged on the common wiring 220 on the terminal B side. If it is necessary to prevent the oscillation circuits from coupling, it is possible to obtain an effect by arranging it on only one side. This makes it possible to obtain a sufficient effect while minimizing the increase in components. Furthermore, by arranging all the inductors 120 to be inserted on the terminal side on one side, it is possible to easily configure the wiring and component arrangement. In addition, when an oscillator or lighting is configured using multiple oscillation circuits, it is possible to miniaturize the oscillator or lighting by forming multiple oscillation circuits on the same chip. On this chip, one terminal of the oscillation circuit is connected to the substrate potential as in the general configuration, so that the present embodiment can be applied without significantly changing the configuration inside the chip from the general configuration. Note that it is not necessary to arrange the inductor 120 on only one terminal, and it is also possible to arrange the inductor 120 on both terminals. It is also possible to arrange the inductor 120 on the terminal B side instead of the terminal A side.

According to this embodiment, in an oscillator driven by the same voltage bias circuit, multiple oscillation circuits (resonators) having negative resistance can be stably oscillated at a desired terahertz frequency.

<Embodiment 2>
As the oscillator 2 according to the second embodiment, the arrangement of the inductors 121, 122, and 123 in the oscillator 1 according to the first embodiment will be described. The oscillator 2 according to this embodiment will be described with reference to Figures 4(A) to 5(B). As shown in Figure 4(A), the oscillator 2 includes a printed circuit board 500 (PCB), a package 501 (PKG), a chip 600, and a voltage bias circuit 200.

As shown in FIG. 4B, the chip 600 includes an oscillator circuit 100 (111, 112, 113) including a negative resistance element 101, and is mounted in a package 501. The chip 600 also includes an antenna 602, wiring 603, an electrode 610, a wire 611, and a wire 612.

As shown in FIG. 4A, package 501, voltage bias circuit 200, and surface mount type (SMD) inductors 121, 122, and 123 in packaged form are arranged on printed circuit board 500. Voltage bias circuit 200 is electrically connected to oscillator circuits 111, 112, and 113 on chip 600 via inductors 121, 122, and 123. This is connected via wiring (not shown) that printed circuit board 500 and package 501 have. Package 501 also holds (supports) chip 600.

As shown in FIG. 4B, the wiring of the chip 600 is electrically connected to the wiring of the package 501 by wire bonding. The wire bonding is achieved by electrically connecting the electrode 610 on the chip 600 to the electrode 610 on the package 501 via the wire 611 or the wire 612.

The chip size of the chip 600 is typically several millimeters square to several tens of millimeters square. In addition, in FIG. 4(A), a configuration in which multiple oscillation circuits are all arranged on one chip 600 is described, but this configuration is not limited, and multiple oscillation circuits may be divided into multiple chips.

FIG. 4(C) is a schematic diagram showing the A1-A2 cross section of FIG. 4(B). As shown in FIG. 4(C), an insulating film 620 is disposed on the chip 600. The oscillation circuit 100 (111) is disposed on the chip 600 in the thickness direction of the insulating film 620 (chip 600), and one terminal is connected to the substrate potential of the chip 600. The other terminal is connected to an antenna 602 disposed on the upper side of the oscillation circuit 100 (111). The antenna 602 is connected to an electrode 610 on the A2 side by a wiring 603 on the chip 600. The reference potential of the chip 600 is connected to an electrode 610 on the A1 side by a wiring 613 penetrating the insulating film. Here, the size of the antenna 602 may be an optimal size according to the oscillation frequency of the terahertz wave, and may be, for example, a size of several hundred micrometers (μm) square to several hundred micrometers (μm) square. Furthermore, the antenna 602 is not limited to being a square antenna, and may be any antenna shape as long as it is capable of emitting terahertz waves.

In addition, in this embodiment, the inductors 121, 122, and 123 are configured as surface mount devices (SMD) on the printed circuit board 500, so that elements having the required parameters can be selected and used as desired. Furthermore, by using the inductors 121, 122, and 123 as surface mount devices, the mounting area can be reduced and the degree of integration can be increased. In this embodiment, the same number of inductors 120 as the number of oscillator circuits 100 are required, so reducing the mounting area is important.

According to this embodiment, even when multiple oscillation circuits having negative resistance are driven by the same voltage bias circuit, an oscillator 2 can be provided with a simple configuration that stably oscillates each oscillation circuit at a desired terahertz frequency.

In this embodiment, the configuration in which the inductors 121, 122, and 123 are arranged on the printed circuit board 500 has been described, but the configuration is not limited to this. As shown in FIG. 5(A), a configuration in which the inductors 121, 122, and 123 are arranged on the package 501 together with the chip 600 can also be used. This eliminates the need to pull out wiring from each oscillator circuit to the outside of the package 501, making it possible to reduce the number of pins on the package 501 and the wiring on the printed circuit board 500. As a result, a compact oscillator can be realized.

In this embodiment, the configuration in which the chip 600 is disposed on the package 501 has been described, but the present invention is not limited to this configuration. As shown in FIG. 5(B), the chip 600 may be disposed directly on the printed circuit board 500. This makes it possible to omit the package 501, and therefore to configure the oscillator using a smaller configuration.

<Embodiment 3>
The oscillator 3 according to the third embodiment differs from the oscillator 2 according to the second embodiment in the arrangement of the inductors 121, 122, and 123. The oscillator 3 will be described below with reference to Figs.

In the oscillator 3, the inductors 120 (121, 122, 123) are disposed on a chip 600 including an oscillation circuit 100 (111, 112, 113) as shown in Fig. 6A. The inductors 120 are connected to the oscillation circuit 100 and an electrode 610 via wiring 603 and wiring 604 on the chip 600.

Figure 6 (B) shows a cross-sectional view of A1-A2 in Figure 6 (A). Figure 7 (A) shows an enlarged view of the periphery of the inductor 120, and Figure 7 (B) shows a cross-sectional view of B1-B2 in Figure 7 (A). As shown in Figure 7 (A), the inductor 120 is formed by winding a metal wiring 605 in a loop shape. One terminal of the metal wiring 605 is connected to the wiring 603. An insulating film 621 is formed on the metal wiring 605, and the central end of the metal wiring 605 is connected to the wiring 606 on the insulating film 621. Furthermore, the central end of the metal wiring 605 is connected to the wiring 604 via the wiring 606. The inductor 120 has a simple configuration in which an insulating film and a metal wiring are formed in a loop, so it can be easily formed on the chip 600 on which the negative resistance element 101 and the like are formed.

In this embodiment, unlike the second embodiment in which the inductor 120 is arranged in the package 501, the inductor 120 is arranged on the chip 600 on which the oscillator circuit 100 is formed, so that an increase in the area of the oscillator can be suppressed. Therefore, even when the same voltage bias circuit drives multiple oscillator circuits having negative resistance, it is possible to provide an oscillator with a compact configuration that stably oscillates each oscillator circuit at a desired terahertz frequency.

Note that the inductor of this embodiment is not limited to the configuration described above, and may be any inductor that can be placed on a chip.

<Embodiment 4>
The oscillator 4 according to the fourth embodiment has a shunt element for preventing parasitic oscillation in addition to the configuration of the oscillator 1 according to the first embodiment. The oscillator 4 according to the present embodiment will be described with reference to the circuit diagrams in Fig. 8(A) and Fig. 8(B).

As shown in FIG. 8A, the oscillator 4 includes a shunt element 900. The shunt element 900 is arranged in series with the negative resistance element 101, and by coupling with the oscillation circuit 100, it prevents coupling with elements external to the oscillation circuit 100. In this way, the shunt element 900 suppresses oscillations other than the desired terahertz oscillation frequency ft of the oscillation circuit 100.

Generally, the wiring connecting the voltage bias circuit 200 and the oscillation circuit 100 includes parasitic inductors and parasitic capacitances (elements 400 to 404), as shown in FIG. 14B. Therefore, an oscillation circuit with a frequency different from the desired frequency ft may be formed between the elements of the oscillation circuit 100 and the parasitic elements of the voltage bias circuit 200, causing parasitic oscillation.

In addition, the voltage bias circuit 200 itself is generally not an ideal voltage source. In detail, as shown in FIG. 14B, the voltage bias circuit 200 has an ideal voltage source 201, a parasitic inductor, a parasitic resistor, a parasitic capacitance, etc. (elements 411, 412, 413). Therefore, parasitic oscillation may occur between the elements of the oscillation circuit 100 and the parasitic elements of the voltage bias circuit 200 other than the voltage source 201.

Therefore, in this embodiment, in order to suppress the parasitic oscillation, as shown in FIG. 8A, the shunt element 900 and the oscillation circuit 100 are arranged in parallel with the voltage bias circuit 200. Here, the shunt element 900 has an impedance that is approximately the same as the resistance value Rr of the negative resistance element 101 of the oscillation circuit 100. As a result, the oscillation circuit 100 and the shunt element 900 are coupled, and a loss can be generated in the shunt element 900. The loss caused by the shunt element 900 prevents the oscillation circuit 100 from coupling with external wiring or the voltage bias circuit 200, and the parasitic oscillation can be suppressed. In addition, the range of the impedance of the shunt element 900 is preferably less than twice the resistance value Rr, and more preferably less than 1.5 times.

Furthermore, the position of the shunt element 900 must be considered. Specifically, the length of the wiring connecting the oscillation circuit 100 (111, 112, 113) and the shunt element 900 is set to 1/4 of the wavelength λ of the maximum frequency (high-frequency cutoff frequency) at which parasitic oscillation is to be suppressed. This is because if the wavelength of the AC signal is short, even a slight change in the position of the wiring will cause a large change in phase, and an equivalent capacitance or equivalent inductance will occur due to reflection at the wiring end. In particular, when trying to suppress parasitic oscillation near frequencies from gigahertz to terahertz, the shunt element 900 is placed near the oscillation circuit. If the distance from the oscillation circuit 100 to the shunt element 900 is 1/4 of the wavelength λ or less, the generation of equivalent capacitance or equivalent inductance due to the effect of reflection at the wiring end can be suppressed, and parasitic oscillation can be suppressed.

In addition, in this embodiment, as shown in FIG. 8B, a capacitive element 901 is used as the shunt element 900. The capacitive element 901 can easily reduce impedance in proportion to the frequency. Therefore, the capacitive element 901 can obtain a continuously low impedance from a specific frequency to a high frequency range. For example, the capacitive element 901 can obtain a low impedance in a wide range from several megahertz to several terahertz, and can suppress parasitic oscillation in that frequency range. However, in the absence of the inductor 120, when multiple oscillation circuits 100 are connected, the capacitive elements 901 are coupled to each other, which causes parasitic oscillation due to coupling between adjacent oscillation circuits 100, and in some cases, oscillation cessation.

In contrast, in this embodiment, the oscillator 4 has inductors 120 (121, 122, 123) between the oscillation circuits 100. This makes it possible to prevent the oscillation circuit 100 and the associated shunt element 900 from coupling to other oscillation circuits 100 or other shunt elements 900.

The oscillator according to this embodiment can suppress parasitic oscillations and stably oscillate each oscillation circuit at the desired terahertz frequency, even when multiple oscillation circuits with negative resistance are driven by the same voltage bias circuit.

<Embodiment 5>
The oscillator 5 according to the fifth embodiment differs from the oscillator 4 according to the fourth embodiment in the configuration of a shunt element that prevents parasitic oscillation. The oscillator 5 according to the fifth embodiment will be described with reference to Figs. 9A and 9B.

In this embodiment, as shown in FIG. 9A, a resistive-capacitive element 902 is used as the shunt element. The resistive-capacitive element 902 is configured by connecting a resistive element 903 and a capacitive element 904 in series.

Although the resistive-capacitive element 902 has more components than the capacitive element 901 according to the fourth embodiment, it can stably suppress parasitic oscillations over a wide frequency range. In addition, since the resistive element 903 and the capacitive element 904 are arranged, no steady-state current flows in the frequency range near DC, and power consumption does not increase.

Here, if no loss occurs in the shunt element, it may not be possible to prevent the oscillation circuit from coupling with other parts. Therefore, when the capacitance element 901 is used as a shunt element as in the fourth embodiment, the impedance decreases as the frequency increases, so that the capacitance value may not be made too large in order to prevent the loss at high frequencies from decreasing too much.

However, in this embodiment, in a frequency range sufficiently higher than the frequency determined by the time constant of the resistive element 903 and the capacitive element 904, the capacitive element 904 is short-circuited, and sufficient loss can be generated in the resistive element 903. Therefore, by including the resistive element 903 in the shunt element, the capacitance value of the capacitive element 904 can be increased, and a certain amount of loss generated in the shunt element can be ensured.

In other words, when the resistive-capacitive element 902 is used as a shunt element, the inclusion of the resistive element 903 makes it possible to increase the capacitance value and obtain sufficient loss even at low frequencies, compared to when the capacitive element 901 is used as a shunt element. Therefore, the oscillator 5 according to this embodiment can suppress parasitic oscillations over a wider range of frequencies.

With the oscillator 5 according to this embodiment, even when multiple oscillation circuits having negative resistance are driven by the same voltage bias circuit, the occurrence of parasitic oscillation can be further suppressed, and each oscillation circuit can stably oscillate at the desired terahertz frequency.

In addition to shunt elements including capacitive elements such as capacitive element 901 and resistive-capacitive element 902, a configuration in which resistive element 905 is used as the shunt element may also be used, as shown in FIG. 9(B).

The configuration using the resistive element 905 as a shunt element is a simple configuration using only a resistor, and compared to a shunt element that includes a capacitive element, it is easier to generate sufficient loss and control the impedance. Therefore, a shunt element consisting of only the resistive element 905 can reduce the possibility of coupling occurring between oscillation circuits compared to a shunt element that includes a capacitive element.

In other words, compared to a configuration in which the resistive element 905 is used as a shunt element, in a configuration in which the capacitive element 901 or the resistive-capacitive element 902 is used as a shunt element, it is more important to avoid the occurrence of coupling between the oscillator circuits. Therefore, it can be said that the inductor 120 is highly effective in suppressing the occurrence of coupling, particularly in shunt elements having capacitance. However, even when the resistive element 905 is used as a shunt element, the effect of suppressing the occurrence of coupling between the oscillator circuits can be sufficiently obtained.

<Embodiment 6>
The oscillator 6 according to the sixth embodiment differs from the oscillators according to the other embodiments in the relationship between the number of shunt elements and the inductor. Other than that, it is the same as a combination of the first to fifth embodiments. The oscillator 6 according to the sixth embodiment will be described with reference to Figs. 10(A) to 11(B).

Figure 10 (A) shows the configuration of oscillator 6, and Figure 10 (B) shows the detailed configuration of chip 600 in oscillator 6. In oscillator 6, as shown in Figures 10 (A) and 10 (B), shunt element 911 is arranged on chip 600, shunt element 912 is arranged on package 501, and shunt element 913 is arranged on printed circuit board 500. Furthermore, inductors 121 to 123 are arranged between shunt element 911 and shunt element 912. Inductors 121' to 123' are arranged between shunt element 912 and shunt element 913. Inductors 121" to 123" are arranged between shunt element 913 and voltage bias circuit 200. In this way, oscillator 6 has multiple inductors in multiple stages, as shown in the circuit diagram in Figure 11 (A).

Each of the shunt elements 911 to 913 is placed close to the oscillation circuit 100 in order to suppress high-frequency parasitic oscillation. More preferably, the distance from the oscillation circuit 100 to each of the shunt elements 911 to 913 is equal to or less than ¼ of the wavelength at the parasitic oscillation frequency suppressed by each of the shunt elements. Here, the frequency at which the shunt element 911 exerts its effect of preventing parasitic oscillation is fs1, the frequency at which the shunt element 912 exerts its effect of preventing parasitic oscillation is fs2, and the frequency at which the shunt element 913 exerts its effect of preventing parasitic oscillation is fs3. The frequencies of the shunt elements are in ascending order from the closest to the oscillation circuit, with a relationship of fs1>fs2>fs3.

In addition, in this embodiment, the impedance (inductance) of the inductor 120 is made smaller in the order of proximity to the oscillator circuit 100. Here, the impedance of the inductor 121 (122, 123) is Zlm1, the impedance of the inductor 121' (122', 123') is Zlm2, and the impedance of the inductor 121" (122", 123") is Zlm3. The relationship Zlm1<Zlm2<Zlm3 holds. Here, the larger the impedance, the larger the size of the inductor. Therefore, if the impedance of the inductor 120 placed on the chip 600 is large, the area of the chip 600 is occupied, so there is an upper limit to the impedance. Also, if the impedance of the inductor 120 placed in the package 501 is large, the size of the package 501 increases due to the increase in the size of the surface-mounted components. In this embodiment, the impedance of the inductor is small in the order of proximity to the chip 600, so the mounting area of the chip 600 and the package 501 can be reduced.

At frequency fs1, impedance Zlm1 has a value that is approximately equal to or larger than impedance Zr1 of the oscillator circuit 100. This allows the shunt element 911 to generate losses at frequencies equal to or higher than frequency fs1, and prevents coupling with external elements. Even at frequencies where the loss caused by the shunt element 911 is insufficient, the inductor 121 (122, 123) can generate losses at the frequency, so that electromagnetic waves at the frequency do not leak out to the outside. The relationship between the shunt element 912 and the inductor 121' (122', 123') and the relationship between the shunt element 913 and the inductor 121'' (122'', 123'') are similar. Here, FIG. 11B shows a schematic diagram of the relationship between the impedances Zlm1 to Zlm3 and the frequency in this embodiment. The impedances Zlm1 to Zlm3 have values that are approximately equal to or larger than the impedance Zr1 in a continuous manner.

In this manner, in this embodiment, by placing an inductor between multiple shunt elements, parasitic oscillation in the shunt elements can be suppressed without causing a significant increase in mounting area. Furthermore, by using multiple shunt elements, parasitic oscillation can be suppressed over a wide range of frequencies. With the oscillator according to this embodiment, even when multiple oscillation circuits having negative resistance are driven by the same voltage bias circuit, the occurrence of parasitic oscillation can be suppressed, and each oscillation circuit can stably oscillate at the desired terahertz frequency.

In this embodiment, the shunt element 911 is arranged on the chip 600, the shunt element 912 is arranged on the package 501, and the shunt element 913 is arranged on the printed circuit board 500. However, this embodiment is not limited to this. It may be configured such that none of the three shunt elements are present, or it may be configured such that four or more shunt elements are arranged.

<Embodiment 7>
In the seventh embodiment, an oscillator 7 having a voltage bias circuit that applies an AC voltage, rather than a voltage bias circuit that applies a DC voltage, will be described.
The oscillator 7 according to this embodiment will be described using the following.

In the first embodiment, the voltage bias circuit 200 that applies a DC voltage is used in the oscillator 1. In the present embodiment, as shown in FIG. 12(A), instead of the voltage bias circuit 200 in the oscillator 7, an AC voltage bias circuit 202 that applies an AC voltage is used.

The AC voltage bias circuit 202 generates an AC voltage to be applied to the oscillation circuit 100. Specifically, as shown in FIG. 12B, the AC voltage bias circuit 202 uses a voltage that changes between an operation voltage Vop that oscillates terahertz waves at a certain frequency fac and a voltage value Voff at which the oscillation of the terahertz waves stops. This allows the oscillation and stopping of the terahertz waves to be repeated at the frequency fac. Note that the voltage value Voff may be any voltage value outside the negative resistance region NR, for example, 0 V. The frequency fac is sufficiently lower than the oscillation frequency of the terahertz waves (from 30 GHz to 30 THz). A frequency in the range of several Hz to several MHz is used for the frequency fac, but other frequencies can also be used as long as there are no problems in use.

By repeatedly oscillating and stopping the terahertz waves, it is possible to repeat the irradiation and non-irradiation states of the terahertz waves. This makes it possible to grasp the offset noise components of the terahertz waves irradiated by other elements when the terahertz oscillation is stopped. Therefore, in a configuration in which an oscillator is used for a camera that irradiates an object with terahertz waves and captures the terahertz waves reflected from the object, it is possible to remove noise components other than those originating from the illumination. This makes it possible to realize a terahertz camera with a high S/N ratio.

The oscillator according to this embodiment can repeatedly oscillate and stop terahertz waves, making it possible to grasp the offset noise components of the terahertz waves. Because the oscillator according to this embodiment can grasp the offset components, it can improve the signal-to-noise ratio when used in lighting or cameras.

In addition, in the configuration using the resistive-capacitive element 902 of the fifth embodiment, the frequency frc determined by the time constant of the capacitive element 904 and the resistive element 905 is required to be higher than the frequency fac at which the AC voltage bias circuit 202 changes. For example, when a rectangular wave voltage is used in the AC voltage bias circuit 202, it is preferable that the frequency frc is several times or more higher than the frequency fac.

<Embodiment 8>
In the eighth embodiment, an imaging device (image acquisition device) using an oscillator will be described. The imaging device according to this embodiment will be described with reference to Fig. 13(A) and Fig. 13(B). The imaging device includes an illumination 801, a terahertz imaging element 802, and a timing generation unit 803.

The illumination 801 is an illumination device that has the oscillator 1 according to the first embodiment and irradiates the object 800 with terahertz waves 811 (predetermined electromagnetic waves). As shown in FIG. 13(A), the terahertz waves 811 emitted from the illumination 801 are reflected by the object 800, which is the subject of the image capture, and the reflected terahertz waves 812 are captured by the terahertz imaging element 802. Since the image that the terahertz imaging element 802 can obtain varies depending on the shape and physical properties of the object 800, the imaging device can appropriately obtain information about the object 800.

According to this embodiment, multiple oscillator circuits are driven by the same voltage bias circuit, and each oscillator circuit can be stably oscillated at a desired frequency, thereby realizing lighting that outputs terahertz waves more stably.

Furthermore, as shown in FIG. 13(B), the lighting 801 can use an oscillator 7 using the AC voltage bias circuit 202 according to embodiment 7.

In FIG. 13B, the imaging device further includes a timing generation unit 803. The timing generation unit 803 outputs a timing signal 810 to the illumination 801 and the terahertz imaging element 802. The timing signal 810 input to the illumination 801 is used to adjust the voltage change timing of the AC voltage bias circuit 202. The illumination 801 periodically repeats oscillation and stopping of the terahertz wave at the adjusted timing, thereby generating a period in which the terahertz wave is irradiated and a period in which it is not irradiated. On the other hand, the timing signal 810 input to the terahertz imaging element 802 performs an operation of imaging the period in which the illumination 801 irradiates the terahertz wave and the period in which it is not irradiated, respectively, and taking the difference between the captured images in each period. This makes it possible to remove the terahertz wave components that are not intentionally irradiated (becoming offset noise components). Therefore, it is possible to improve the signal-to-noise ratio (SNR) of the acquired image.

When the terahertz wave oscillator circuit according to this embodiment is used in the lighting 801, multiple oscillator circuits are driven by the same AC voltage bias circuit, and each oscillator circuit can stably oscillate at the desired frequency. Therefore, even if irradiation is repeatedly started and stopped, it is possible to obtain illumination with a large and stable terahertz output, and when used in an image acquisition device, images with a high signal-to-noise ratio can be acquired.

1: oscillator, 100: oscillation circuit, 101: negative resistance element,
120: inductor, 200: voltage bias circuit

Claims (15)

A plurality of resonators each having a negative resistance element;
a voltage bias circuit that applies a voltage to the plurality of resonators;
a shunt element disposed in parallel with any one of the plurality of resonators with respect to the voltage bias circuit;
having
the plurality of resonators are connected in parallel to the voltage bias circuit via separate inductors,
At a predetermined frequency or higher, the impedance of the inductor is greater than an absolute value of the impedance of a resonator among the plurality of resonators that corresponds to the inductor;
In the shunt element, a resistive element and a capacitive element are connected in series.
1. An oscillator comprising: A plurality of resonators each having a negative resistance element;
a voltage bias circuit that applies a voltage to the plurality of resonators;
having
the plurality of resonators are connected in parallel to the voltage bias circuit via separate inductors,
At a predetermined frequency or higher, the impedance of the inductor is greater than an absolute value of the impedance of a resonator among the plurality of resonators that corresponds to the inductor;
A plurality of shunt elements are connected in parallel to each of the plurality of resonators,
The plurality of shunt elements are connected to each other via the inductor.
1. An oscillator comprising: The shunt element is composed of a capacitance element.
3. The oscillator according to claim 2 . In the shunt element, a resistive element and a capacitive element are connected in series.
3. The oscillator according to claim 2 . the shunt element and the resonator arranged in parallel with the shunt element with respect to the voltage bias circuit are connected by a wiring having a length of ¼ or less of a wavelength corresponding to a cutoff frequency on the high frequency side;
5. An oscillator according to claim 1, wherein the first and second electrodes are arranged in a first direction. the inductor is disposed on one terminal side of each of the plurality of resonators, and is not disposed on the other terminal side;
6. An oscillator according to claim 1, wherein the first and second electrodes are arranged in a first direction. The predetermined frequency is 10 KHz or more.
7. An oscillator according to claim 1, wherein the first and second electrodes are arranged in a first direction. The inductor is disposed on a chip including the plurality of resonators.
8. An oscillator according to claim 1, wherein the first and second electrodes are arranged in a first direction. The inductor is disposed on a package or a printed circuit board that holds a chip including the plurality of resonators.
8. An oscillator according to claim 1, wherein the first and second electrodes are arranged in a first direction. the voltage bias circuit applies an AC voltage to the plurality of resonators;
10. An oscillator according to claim 1 , wherein the first and second electrodes are arranged in a first direction. The plurality of resonators generate electromagnetic waves having frequencies in the range of 30 GHz to 30 THz.
11. The oscillator according to claim 1 . the negative resistance element is a resonant tunneling diode;
12. An oscillator according to any one of claims 1 to 11 . Further comprising a package, a printed circuit board, and a surface mount device.
13. An oscillator according to any one of claims 1 to 12 . The plurality of resonators are disposed on a chip,
The size of the tip is from several millimeters square to several tens of millimeters square.
14. An oscillator according to any one of claims 1 to 13 . A lighting device comprising an oscillator according to any one of claims 1 to 14 ;
an imaging element for imaging an object irradiated with the electromagnetic wave generated by the oscillator;
Equipped with
1. An imaging device comprising:

Images